1. Field of the Invention
The present invention relates to glass members for use in the cathode ray tube including a glass panel, glass funnel and glass bulb for TV sets and the like, and particularly to a glass panel and a glass funnel having improved shapes in their seal ends and therearound.
2. Description of the Related Art
Referring now to FIGS. 10 and 11, the conventional cathode ray tube has a glass panel 1x′ (hereinafter simply referred to “panel”), a glass funnel 1y′ (hereinafter simply referred to “funnel”), and a neck tube 11y′ fused to the smaller opening of the funnel 1y′, as major glass members.
The panel 1x′ has a face part 2x′ having an effective plane on which images are to be displayed, and a skirt part 4X′ surrounding the face part 2x′ and standing at almost right angles via a blend R part 3x′ at the peripheral edge of the face part 2x′. The skirt part 4x′ has side parts 6x′ connected at four corner pats 5x′, and a seal end face 7x′ is formed at the opening end of each side part 6x′ for connection with the funnel 1y′. 
Meanwhile, the funnel 1y′ of a funnel-like shape has a yoke part 3y′ having a small opening end 2y′ to which the neck tube 11y′ is to be fused, and a body part 4y′ integral with the yoke part 3y′. The body part 4y′ has side parts 6y′ connected at four corner parts 5y′, and a seal end face 7y′ is formed at the large opening end of each side part 6y′ for connection with the panel 1x′. 
The panel 1x′ and the funnel 1y′ are molded by putting a lump of high-temperature molten glass called glass gob in a female mold consisting of a bottom mold and a shell mold and then pushing a male mold (plunger mold) thereon to press and develop the lump of the molten glass. When the lump of the molten glass is molded into a predetermined shape, the plunger mold is lifted and the glass molded article is appropriately cooled and solidified. After the shell mold is removed, the glass molded article, namely the panel 1x′ or funnel 1y′ is released from the bottom mold.
During this process, with respect to the seal end faces 7x′ and 7y′ of the panel 1x′ and the funnel 1y′ and their peripheries, their outer walls and seal end faces are shaped by the concave portion of the shell mold, while their inner walls are shaped by the convex portion of the plunger mold. For easy removal from the shell mold and plunger mold after molding, the peripheries of the seal end faces 7x′ and 7y′ are shaped to become slightly thinner to the top edge from mold match lines Mx′ and My′, which correspond to the mating faces-between the shell mold and the bottom mold (see FIG. 12).
After the panel 1x′ and the funnel 1y′ thus formed go through subsequent prescribed treatments, their seal end faces 7x′ and 7y′ are fused together and thereby a glass bulb (hereinafter simply referred to “bulb”) for a cathode ray tube (CRT) is provided. In the bulb, necessary components are installed to complete a cathode ray tube, and the tube is evacuated to keep a high vacuum.
As the methods for fusing the panel 1x′ and the funnel 1y′ together, it is common that the seal end faces 7x′ and 7y′ are heated up and softened, and then directly mated together for fusion. It is also a common practice to use frit glass (solder glass) in between the seal end faces 7x′ and 7y′ for fusion.
Projector-use cathode ray tubes and monochrome-use cathode ray tubes do not need internal members such as a shadow mask or aperture grill that are essential in the direct-view type color cathode ray tube. Thus, particularly when manufacturing bulbs for projector-use cathode ray tubes and monochrome-use cathode ray tubes, the seal end faces 7x′ and 7y′ are heated with burners and softened and then directly pushed onto each other for easy, cost-saving fusion.
Now the details of the peripheral shape of each seal end face 7x′, 7y′ of the panel 1x′ or the funnel 1y′ will be described with reference to FIG. 12. Thickness t1′ of the glass, for instance, 1 mm away along the tube axis from the top of the seal end face 7x′, 7y′ is slightly smaller than thickness T′ of the glass at mold matching line Mx′, My′ on the side part 6x′, 6y′ of the skirt 4x′ or the body 4y′. In fact, t1′ is substantially equal to T′.
This is a result of the need to meet a requirement that the mold design should be easy or simple while maintaining the easiness of glass release from the shell mold and plunger mold after molding.
However, under a recent need for increased productivity, if the seal end faces 7x′ and 7y′ have the peripheral shapes like those shown in FIG. 12, the productivity per unit time cannot be raised when manufacturing bulbs by fusing the panel 1x′ and the funnel 1y′. 
When the panel 1x′ and the funnel 1y′ are heated to soften the seal end faces 7x′ and 7y′, the heat provided by burners and the like propagates from a surface near the seal end face 7x′ and 7y′ to the inside. The glass is heated up and softened when an appropriate amount of heat has been conveyed. As shown in FIG. 12, if the glass thickness is substantially the same from mold match line Mx′, My′ to the seal end face 7x′, 7y′, it takes a long time for heat conduction and glass softening because the seal end face 7x′, 7y′ are thick. As a result, the productivity does not rise.
To avoid this problem, the glass extending from mold matching line Mx′, My′ to the seal end face 7x′, 7y′ should be made thin. However, if the glass is simply made thin, a strength problem may arise because the bulb is evacuated to keep a high vacuum. Thus there is a limit to thinning of the glass wall to maintain mechanical strength.
In detail, as disclosed in Japanese Patent Publication No. Sho 43-7608, it has been a common practice probably with no exception to make the rate of decreasing thickness of glass extending from mold match lines Mx′, My′ to the seal end faces 7x′, 7y′ equal or almost equal to that of glass on the top side (side of the seal end faces 7x′, 7y′). Namely, if easiness in mold release after molding and in mold design is considered, the rate of decreasing glass thickness toward the top side must be constant or almost constant, and the above conventional shape has been regarded as the standard design shape.
As a result, if the thickness of a target glass portion is to be made thin, the rate of decreasing glass thickness toward the top side has been made constant or almost constant over the entire range. Then the glass particularly on the top side becomes too thin, and a strength problem may arise as described above.